A simple method is proposed to calculate the stress intensity factors of two dimensional Mixed mode (I+II) problems, using the crack face displacements. In this method the differences in crack face displacements perpendicular to the crack plane is used to calculate the stress intensity factors. The displacement components in this method are obtained using finite element method, incorporating quarter point elements at the crack tip. The performance of the proposed method is evaluated for linear elastic centre cracked plate under mixed mode I + II loading. The results were in good agreement with that of the published bench mark problem. From the convergence studies, the present method could evaluate the SIF accurately and efficiently, compared to other methods. The other advantages of the present methods are its simplicity in expression and implementation and there by less computational effort. Also the displacement based method requires less mesh refinement in comparison with that of the stress based method.

Keywords: Stress intensity factor, Fracture mechanics, Crack propagation, Mixed mode, Displacement methods, Finite element analysis.